The invention concerns a rotatable cutting bit, as well as the bit holder, wherein the cutting bit has a hard insert at the forward end thereof. The cutting bit rotatably mounts in the bit holder. More specifically, the invention pertains to such a rotatable cutting bit, as well as the bit holder, designed so as to exhibit a reduction in the tendency for debris to impede rotation, and thereby provide for improved rotation, between the bit and the bit holder. The invention also provides for a rotatable cutting bit, as well as the bit holder, which provides for improved wear protection for the bit holder during operation.
In the past, rotatable cutting tools have been put to a number of uses, including use as a mine tool in a continuous mining machine. Typically, a continuous mining machine includes a driven rotatable drum having a plurality of support blocks affixed thereto. Each block contains a central bore therein.
Earlier rotatable cutting tools used in continuous mining applications typically comprised an elongate steel body with a hard cemented carbide tip brazed into a socket contained in the forward end of the steel body. The steel body included a reduced diameter portion adjacent the rearward end thereof. A retainer was positioned adjacent the reduced diameter portion of the steel body and functioned to rotatably retain the rotatable cutting tool within the bore of the support block during operation.
In operation, the drum rotated whereby the rotatable cutting tools impacted the earth formation, such as, for example, coal, so as to cut and break up the earth formation. As can be appreciated, the earlier rotatable cutting bits operated in an environment in which small particles of the earth formation impacted by the bit, such as coal, impinged upon the cutting bit. As the length of operation increased, these contaminants or debris had the tendency to become sandwiched between the rotatable cutting bit and the bit holder. If the amount of contaminants or debris became too great, it impeded the rotation of the cutting bit. When the cutting bit failed to rotate or the rotation of the cutting was impeded, the cutting bit experienced premature and uneven wear, which resulted in the shortening of the expected useful life of the cutting bit. It is, therefore, apparent that in light of the past experience of earlier cutting bits, it would be beneficial to provide a rotatable cutting bit which has an improved ability to freely rotate during operation, and furthermore, is less susceptible to debris-generated non-rotation than earlier cutting bits.
During the operation of the earlier cutting bits, the support block experienced wear due to the contact between the cutting bit and the support block, as well as the impingement of the debris from the cutting operation. While the cutting bit was replaced on a periodic basis after the expiration of the useful life thereof, the support block was typically intended to be functional much longer than the cutting bit. As the bore and front face of the support block became worn, the support block lost its effectiveness due to deformation and wear of the bore and the front face thereof. In the case of the bore, it lost its initial cylindrical shape by becoming out-of-round, oversized or bell-mouthed. In the case of the front face of the support block, it lost its flatness. Each one of these conditions impeded the satisfactory rotation of the cutting bit in the support block.
It would, therefore, be very advantageous to provide a cutting bit which, during operation, protects the bore of the bit holder, as well as the front face of the support block, from deformation. By providing this protection, a cutting bit would help prolong the useful life of the support block, as well as, help the rotation of the cutting bit.
In the past, others have tried to provide for improved rotation of the cutting bit relative to the bit holder. One early patent is U.S. Pat. No. 4,201,421, to DenBesten et al., which discloses a rotatable cutting bit having a split sleeve retainer with or without a collar. According to the DenBesten et al. patent, this style of retainer helps prevent wear between the cutting bit and the bit holder. The DenBesten et al. sleeve does not rotate relative to the cutting bit or the bit holder during operation. Thus, there is only one surface interface which, if clogged with debris, will cause the cutting bit to not rotate.
U.S. Pat. No. 4,561,698, to Beebe, shows a rotatable cutting bit which has a retainer comprising a sleeve and a flange which extends over the face of the support block. Like the retainer of the DenBesten et al. patent, this retainer engages the wall of the bore in the support block so that it does not rotate during operation. Like the cutting bit of DenBesten et al., there is only one surface interface which, if clogged with debris, will cause the cutting bit to not rotate. U.S. Pat. No. 4,844,550, to Beebe, shows a cutting bit like that of the '698 Beebe patent, as well as a retainer comprised of a sleeve and a collar. Neither the sleeve nor the collar appears to rotate during operation of the cutting bit so that the cutting bit of the '550 patent appears to have the same drawbacks as that of the '698 patent.
U.S. Pat. No. 3,865,437, to Crosby, appears to show a cutting bit which is rotatably received by a sleeve. The sleeve is rotatably received in the bore of a support block.
All Pacific Distribution Company, of Anaheim, Calif., has advertised for sale a so-called Spin-Shield. According to the advertisement, the Spin-Shield appears to be made of hard material and rests between the cutting bit and the block. The shield protects the face of the support block from wear. U.S. Pat. Nos. 4,660,890 and 4,823,454, to Mills, appear to show a shield which protects the face of the support block during operation. These patents also discuss the Spin-Shield structure.
In trying to design a cutting bit-bit holder assembly, one should try to stay within the basic dimensional boundaries, i.e., the design envelope, defined by the volume of the earlier cutting bit-bit holder assemblies. This restriction regarding the design envelope is important so that there exists compatibility with the existing continuous mining machines. Furthermore, it is advantageous to maintain the current design envelope in order to not impede the flow of cuttings or debris produced during the cutting operation. This restriction regarding the design envelope, however, results in certain drawbacks in the earlier assemblies.
For example, FIG. 1 of the present application shows an earlier cutting bit-bit holder assembly that comprises a support block with a thick rotatable sleeve having a thick axially forward flange. A cutting bit is within the bore of the sleeve. In this assembly, the sleeve rotates relative to the support block and the cutting bit.
Because the sleeve is thick, the thickness of the material in the support block providing support for the bore must be reduced so as to maintain the design envelope. As a consequence, there is less material to support the cutting bit within the support block which weakens the support to the cutting bit provided by the support block.
Because the flange of the sleeve is thick, there is an increase in the distance between the tip of the cutting bit and the face of the support block. This increase in distance causes excessive loading forces on the support block during operation.
As another example, FIG. 2 of the present application shows an earlier cutting bit assembly that comprises a bit holder which comprises a support block, a bushing pressed into the bore of the support block, and a replaceable sleeve within the bore of the bushing. The cutting bit is within the bore of the sleeve. The sleeve rotates with respect to the cutting bit and the bushing.
Like for the example of FIG. 1, because the combined thickness of the sleeve and the bushing is relatively large, the thickness of the material in the support block providing support for the cutting bit must be reduced so as to maintain the design envelope. As a consequence, there is less material to support the cutting bit, which weakens the support provided by the support block.
Because the flange of the sleeve is thick, there is an increase in the distance between the tip of the cutting bit and the face of the support block. Like the example of FIG. 1, this increase in distance causes excessive loading forces on the support block during operation.
It can thus be appreciated that earlier cutting bits, and bit holders, have suffered from disadvantages associated with the exertion of excessive loading forces on an already weakened support block. It would, therefore, be advantageous to provide a rotatable cutting bit, and bit holder, that reduces the above-mentioned drawbacks and also provides for improved rotational characteristics, deformation resistance, and wear resistance.